Methods and apparatus for implementing transmissive display devices

ABSTRACT

Energy efficient transmissive and transreflective display devices are described. Ambient light from a natural or artificial source is used to replace and/or supplement light normally supplied by a backlight. This is done by directing ambient light to the rear of a transmissive display panel. A window, light tunnel, or a reflective surface located in the rear or top of a display device may be used to direct the ambient light to the back of the display panel. A translucent diffuser and/or diffuse reflector are used to diffuse the ambient light to reduce the chance of bright spots appearing on the display. Additional energy efficiency is achieved by using one or more photo-sensors to detect the amount of light, incident on the front and/or rear of a display panel and by automatically adjusting the backlight intensity as a function of photo-sensor output. In this manner, backlight intensity can be minimized while maintaining the viewability of images shown on the display. In such an embodiment, energy savings are achieved as compared to devices which use fixed backlight intensity settings in a variety of light conditions. Control of the power supplied to a display&#39;s backlight in accordance with the present invention can reduce electrical energy consumption and prolong the amount of time a portable device can be used before its batteries need to be recharged.

CROSS REFERENCES TO RELATED APPLICATIONS

[0001] This application is a divisional application of application Ser.No. 09/299,521, filed Apr. 26, 1999. This application is related toco-pending U.S. Patent Application LCD WITH POWER SAVING FEATURES Ser.No. 09/299,522, filed Apr. 26, 1999.

FIELD OF THE INVENTION

[0002] The present invention relates to methods and apparatus forimplementing display devices and, more particularly, to methods andapparatus for reducing the amount of electrical power required bydisplay devices, e.g., transmissive and/or transreflective liquidcrystal display (LCD) devices.

BACKGROUND OF THE INVENTION

[0003] Displays are found in numerous commercial and consumer devices.Because of various physical characteristics, flat panel displays tend tobe favored over cathode ray tube (CRT) displays in many applicationswhere size, weight and/or power consumption is of concern.

[0004] Flat panel displays, including e.g., liquid crystal display (LCD)devices come in many different sizes. Small LCD devices are used inapplications ranging from calculators and wristwatches to point-of-saleterminals and gas pumps. Larger LCD devices are found in portablecomputers, desktop computer displays, and numerous other devices.

[0005] Known LCDs are frequently implemented as reflective,transmissive, or transflective devices. A reflective LCD, as the nameimplies, uses reflection to illuminate the display. FIG. 1 illustrates aknown reflective LCD 102. The reflective LCD 102 includes a closedhousing 109 which contains a liquid crystal cell 104 and a reflector110. A screen 105 made of, e.g., glass, is used to seal the front of theclosed housing 109. Light from an external light source 106 passesthrough the screen 105, liquid crystal cell 104 and is then reflectedback towards the eye 108 by the reflector 110 located behind the liquidcrystal cell 104. The liquid crystal cell includes, for example, frontand rear polarizers with a layer of liquid crystal material sandwichedthere between. The light absorptive characteristics of the liquidcrystal cell are varied by changing an electric field applied to thelayer of liquid crystal material. Thus, by varying an electric fieldimages may be displayed on the LCD 102 and perceived by a viewerrepresented by the eye 108.

[0006] Reflective LCDs are generally the least expensive type of LCD anduse the least amount of power. Reflective LCDs rely on ambient, e.g.,external natural or artificial light sources for illumination.Accordingly, reflective LCDs do not include a backlight. Such displaysoperate satisfactory in well lit locations. However, because they lackan internal light source they are difficult to read in low lightconditions which are often encountered indoors. For this reason,reflective displays have not found wide spread use in portable computersor other devices which may need to be used in low light conditions.

[0007] Transmissive LCDs such as transmissive LCD 103, illustrated inFIG. 2, use an internal light source 107, referred to as a backlight,for illumination. In the transmissive LCD 103, the backlight 107 isenclosed in an opaque housing 110 behind the liquid crystal cell 104 anddisplay screen 105. Light from the backlight 107 passes through theliquid crystal cell 104 and display screen 105 before being perceived bya viewer, represented by the eye 108. Since the housing 110 is opaque,natural and/or ambient light from behind the housing is prevented fromentering the liquid crystal cell from the rear of the housing.

[0008] Transmissive displays are well suited for use indoors underartificial lighting. For this reason, transmissive LCDs are frequentlyused in, e.g., portable computers and lab instruments. One drawback totransmissive displays is that they consume a relatively high amount ofpower due to the use of the backlight. In portable devices such asbattery powered notebook computers, minimizing power consumption isimportant. Power consumption by the backlight is a major factor indetermining the amount of time portable computers can be used betweenrecharges.

[0009] Many portable computers include a brightness control which allowsthe intensity of the backlight used in a transmissive display to bemanually adjusted by a system user. While manually adjusting the displaybrightness to the minimum setting which is acceptable to the user for aparticular set of room conditions can maximize the time before thecomputer needs recharging, users are not accustomed to adjusting thebrightness of their displays each time they move to a different room orambient lighting conditions change. To allow for a transmissive displayto be used in a wide range of conditions, the brightness of the displayis normally set to a value which exceeds the brightness required fornormal room conditions, e.g., so that the display can be used in higherthan normal lighting conditions without having to adjust the brightness.Unfortunately, such intensity settings tend to waste power which, asdiscussed above, is a limited resource in the context of most portabledevices.

[0010] Since the amount of power delivered by batteries is often afunction of their size and thus weight, it is desirable to minimizepower consumption requirements in portable devices to allow for longerperiods of use between battery recharges and/or the use of smaller,lighter, batteries. It is desirable that any methods and apparatusdirected to power conservation be at least partially automated so that auser need not make display adjustments each time lighting conditionschange.

[0011] In addition to relatively high power consumption, anotherdisadvantage of the known transmissive LCD 103 is that such displays areusually hard to read in direct sunlight. The difficulty in reading suchdisplays in direct sunlight arises from the fact that incident sunlightreflected from the display screen 105 can be quite bright compared tothe intensity of the light, originating from the backlight 107.

[0012] While some manufacturers of transmissive LCDs have incorporatedhigh output backlight to enable out of doors use of transmissivedisplays, the relatively high power consumption of such devices rendersthem unsuitable for most battery powered applications.

[0013] Another type of known LCD device is the transflective LCD 111illustrated in FIG. 3. Transflective LCD 111 combines features of thereflective and transmissive LCDs discussed above. As illustrated, atransflective LCD 111 includes a liquid crystal cell 104, partiallytransmissive reflector 116 and a backlight 107. The transflectivedisplay components are enclosed in an opaque housing 114 which is sealedin the front with a screen 105. Behind the screen 105 is the liquidcrystal cell 104, transmissive reflector 116 and backlight 107. Becausethe housing 114 is opaque, it prevents external, e.g., natural orambient light from entering from the rear of the housing.

[0014] In the transmissive display 111, the reflector is normally awhite or silver translucent material that reflects some of the ambientlight entering from the front, i.e., viewing side or surface, of thedisplay 106 while still allowing light from the backlight 107 to passthrough. Transflective LCD 111 is useful in a wide range of lightingconditions. For this reason, LCD 111 is frequently used where a displaymust function in both day and night light conditions, e.g., in gasstation pump displays. Transflective displays suffer from some of thesame power consumption problems, associated with the use of a backlight,discussed above in regard to transmissive displays. In addition,transflective displays tend to have relatively poor contrast ratiossince partially transmissive reflector 116 must be partially transparentto let light from the backlight through.

[0015] In view of the above discussion it is apparent that there is aneed for improved displays, e.g., LCD displays, which can be viewedeasily in a wide range of light conditions. It is desirable that atleast some of the new displays be capable of implementation without abacklight and the power consumption associated therewith.

[0016] From the above discussion, it is also apparent that there is aneed for methods and apparatus directed to reducing the amount of powerutilized by displays which incorporate backlights.

SUMMARY OF THE PRESENT INVENTION

[0017] The present invention is directed to methods and apparatus forreducing the amount of electrical power consumed by display devices,e.g., transmissive and/or transreflective liquid crystal display (LCD)devices.

[0018] One feature of the present invention is directed to automaticallycontrolling the intensity of a backlight as a function of ambient, e.g.,external, light levels. In accordance with this feature of the presentinvention, the ambient light intensity at the front, e.g., viewingsurface, of an LCD is sensed using a sensor and the intensity of thebacklight is automatically adjusted as a function of the sensed lightintensity.

[0019] By adjusting backlight intensity as a function of ambient lightconditions backlight power consumption can be minimized whilemaintaining a satisfactory level of image visibility over a wide andpossibly changing range of light conditions.

[0020] Another feature of the present invention is directed toconserving power through the use of ambient light which is allowed toenter a display device through a non-viewing surface, e.g., the rear ofa display, as opposed to the viewing surface, e.g., front of the displaywhere the screen is located. In one such embodiment of the presentinvention, a transparent window is located in a non-viewing side, e.g.,the rear, of a display device behind a liquid crystal cell.

[0021] In some embodiments a backlight is used to supplement the lightreceived via the opening in the rear of the display device. Bypositioning the back of the display device so that it is directedtowards a natural or artificial light source found in the device'ssurroundings, the need for a light from a powered backlight is reducedor eliminated.

[0022] In one embodiment which utilizes a combination of a backlight andnatural light that is allowed to enter through a non-viewing surface,e.g., rear of the display device, a light sensor is included on both thefront and rear of the display device. The intensity of the backlight isautomatically controlled, as a function of the difference between thelight intensity measured at the front and rear of the display device. Inthis manner, backlight power consumption is automatically adjusted andcontrolled so that the backlight outputs the minimum amount of powerrequired to achieve a user selected degree of visibility. With suitablerear lighting, the backlight may, in such an embodiment, be turnedcompletely off.

[0023] One feature of the present invention is directed to allowing auser of a display device to set the brightness of the display and havethat level maintained under a variety of light conditions withoutrequiring further operator intervention. This result is achieved invarious embodiments by allowing the user of the display to set thedesired brightness and then automatically adjusting backlight intensity,as a function of sensed light intensity, so that the display will beperceived as having the degree of brightness to which the display wasset despite changing light conditions.

[0024] In one embodiment, a user may select normal and power savingbrightness settings. The power saving brightness setting is less thanthe normal brightness setting, e.g., the minimal brightness which theuser considers adequate for viewing. The user can select, e.g., via adisplay switch or software command, either of the two supportedbrightness settings. For example, when on long trips the power savingbrightness setting may be selected while during office use, the normalbrightness setting may be used. In accordance with the present inventionthe selected brightness setting is maintained as a function of one ormore sensed light intensity levels. Thus, the desired brightness settingcan automatically be maintained under a wide range of light conditionswithout requiring user adjustments of brightness levels.

[0025] Numerous additional features, embodiments, and advantages of themethods and apparatus of the present invention are set forth in thedetailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026]FIG. 1 illustrates a known reflective LCD device.

[0027]FIG. 2 illustrates a known transmissive LCD device.

[0028]FIG. 3 illustrates a known transreflective LCD device.

[0029]FIGS. 4-6 illustrate transmissive displays implemented inaccordance with the present invention.

[0030]FIG. 7 illustrates a transmissive display of the present inventionwhich incorporates a backlight.

[0031]FIG. 8 illustrates a transreflective display implemented inaccordance with another exemplary embodiment of the present invention.

[0032]FIGS. 9 through 11 illustrate a portable computer incorporating adisplay implemented in accordance with the present invention.

[0033]FIG. 12 illustrates a portable computer including a light sensorand intensity control circuit implemented in accordance with anotherembodiment of the present invention.

[0034]FIG. 13 illustrates a transmissive display device of the presentinvention which includes a plurality of light sensors and an intensitycontrol circuit.

[0035]FIG. 14 illustrates a portable computer implemented using aplurality of light sensors and an intensity control circuit.

[0036]FIG. 15 is a frontal view of the portable computer illustrated inFIG. 14.

DETAILED DESCRIPTION

[0037] As discussed above, the present invention is directed to methodsand apparatus for reducing the amount of electrical power required bydisplay devices, e.g., LCDs.

[0038] In the description which follows, for the purposes of brevity,elements which are the same as, or similar to one another, will beidentified using the same reference numerals. In addition, arrows willbe used to illustrate rays of light which may be emitted by, e.g., anatural or artificial light source.

[0039]FIG. 4 illustrates a transmissive display device 200 implementedin accordance with one embodiment of the present invention. The display200 comprises, e.g., a transmissive display panel 206 which comprises aprotective outer layer, i.e., the screen 105, and an inner layer,implemented as a liquid crystal cell 104. A translucent diffuser 208 anddiffuse reflector 210 are positioned behind the display panel 206 in anangular arrangement to form a back portion and a bottom portion,respectively, of the display 200. Sides (not shown) coated with areflective material may be used to seal the remaining rear portion ofthe display 200 positioned behind the liquid crystal display 206. Notethat in use, a viewer represented by the eye 108 is positioned in frontof the display panel 206. The rear of the display 200 is positionedfacing the highest intensity ambient light source present, e.g., the sun202. In such an arrangement, ambient light is allowed to pass throughthe translucent diffuser 208 and is reflected by the diffuse reflector210 onto the non-viewing side, e.g., rear, of the display panel 206.

[0040] In such an arrangement, the high intensity ambient light passingthrough the display panel 206 from the rear should be greater than theamount of ambient light reflected from the viewing side, e.g., front, ofthe display panel 206. Such an embodiment allows for viewing of thedisplay in high intensity sunlight and other high intensity ambientlight conditions without the need for a powered backlight. The use ofthe translucent diffuser 208 and diffuse reflector 210 help to eliminatebright spots by diffusing the ambient light before it passes through thedisplay panel 206.

[0041] It is contemplated that a wide variety of plastic and non-plasticmaterials may be used to implement the translucent diffuser 208 anddiffuse reflector 210. In one embodiment, a translucent plastic materialwas used as the translucent diffuser 208 while a white sheet of paperwas used as the diffuse reflector 210.

[0042] As will be appreciated, in portable applications it is desirablethat a display be capable of being stored in a relatively small space.Specifically, in portable computer applications it is generallydesirable that a display be relatively thin, e.g., no more than a fewinches in thickness, and be capable of being folded down flat, e.g.,over a computer keyboard.

[0043]FIGS. 5 and 6, illustrate embodiments wherein displays 203 and 205of the present invention, are implemented using hinged panels capable ofbeing folded to form a flat assembly for storage and transport purposes.

[0044] In the FIG. 5 embodiment, the diffuse reflector 210 is attachedto the bottom of the display screen 206 via a first hinge 212 while therear translucent diffuser 208 is attached to the top of the displaypanel 206 via a second, e.g., top, hinge 214. FIG. 5 illustrates thedisplay 203 deployed for use. When deployed, the display 203 assumes,when viewed from the side, a triangular shape similar to that of thedisplay 200. In order to make the display 203 easy to deploy, sideswhich would otherwise be used to close off the cavity formed by thediffuser 208, diffuse reflector 210 and display panel 206 are omitted.When not in use, the translucent diffuser 208 may be folded back on topof the display panel 206 which can then lie flat against the diffusereflector 210. Alternatively, the translucent diffuser 214 can bepositioned between the display 206 and the diffuse reflector 210 to forma flat assembly with the diffuse reflector 210 on the bottom, diffuser208 in the middle and the display panel 206 on top.

[0045]FIG. 6 illustrates another display 205 which can be folded flat.In this embodiment, the second hinge 214 is eliminated and thetranslucent diffuser 208 is secured directly to the back of the displaypanel 206. A first hinge 212 is located at the intersection of thebottom of the combined display panel/diffuser assembly and the diffusereflector 210. The first hinge 212 is used to allow the folding down ofthe display panel assembly to form a flat display for storage and/ortransportation purposes.

[0046] The displays illustrated in FIGS. 4, 5 and 6 eliminate the needfor a backlight through the use of ambient light for illuminationpurposes. However, in low light conditions, or in conditions where lightis generally of uniform intensity in all directions, use of asupplemental light source, e.g., a backlight, may be desirable.Accordingly, the use of a backlight to supplement ambient lighting iscontemplated and employed in various embodiments of the presentinvention.

[0047] In various embodiments, the display panels 206 used in the FIGS.4-6 embodiments are mounted in housings which support the display panel206 and provide a point of attachment for the first hinge 212. In suchan embodiment, the housing may be considered part of the display panel206.

[0048]FIG. 7 illustrates a back lit transmissive display 302 implementedin accordance with one embodiment of the present invention. The display302 includes a display panel 206 behind which a backlight 207 islocated. The backlight 207 is located in a housing which utilizesdiffuse reflectors 210 for sidewalls and a translucent diffuser 208 toclose the rear of the housing. The diffuse reflectors 210 act as a lightpipe and serve to direct ambient light entering through the reartranslucent diffuser 208 so that it passes out through the display panel206. While the translucent diffuser 208 is illustrated directly behindthe liquid crystal display, use of the light pipe formed by the diffusereflectors 210 allows for the translucent diffuser to be positioned atvarious locations that are not necessarily located directly behind thedisplay panel 206. For example, the translucent diffuser 208 may bepositioned at the top of a device incorporating the display 302 or at aposition off-set from the display panel 206.

[0049] The techniques of the present invention involving the use ofambient light can be applied to virtually any type of device which usesa backlight. FIG. 8 illustrates a transreflective display 304implemented in accordance with the present invention. Note how in theFIG. 8 embodiment, the solid (non-translucent) rear of the knowntransreflective display 111 is replaced with translucent material 208 toproduce the display 304. In the FIG. 8 embodiment, the translucentmaterial 208 allows natural or artificial ambient light to supplement orreplace the light produced by the backlight 207.

[0050]FIG. 9 illustrates a portable computer device 400 implemented inaccordance with the present invention. The computer device includes abase portion 406 for housing a CPU, memory, a keyboard, etc, and a lidportion including first and second panel assemblies 402, 404. A hinge408 is used to connect the lid portion of the computer 400, to the baseportion 406. The hinge 408 allows the lid portion to be raised, e.g.,when the computer is in use, and lowered e.g., for storage and/or duringtransport.

[0051]FIG. 10 illustrates the computer system 400, with the lid portionin the raised position. In this position, the keyboard 407 included inthe base portion 406 is both visible and accessible to a user of thecomputer 400.

[0052]FIG. 11 illustrates the computer system 400 arranged for use. Inthe FIG. 11 arrangement the upper portion of the lid 402 has beenlowered to a fully open position. The upper portion 402 is positioned inFIG. 11 so that it extends parallel to the base portion 402. The upperlid panel 402 includes an inner diffuse reflector 210 and an outerprotective layer 212 made of an opaque material. The lower panel 404 ofthe lid comprises an outer diffuser panel 208 which is secured to aninner display panel 206.

[0053] The upper panel 402 of the lid is positioned at an angle relativeto the upper lid panel 402 so that ambient light falling on the upperlid panel will be reflected by the diffuse reflector 210 through thediffuser panel 208.

[0054] In order to supplement the natural illumination supplied to therear of the display panel 206, in the FIG. 11 embodiment, an optionalbacklight 410 is incorporated into the diffuser panel 208. The backlightis positioned so that its light output is directed through the displaypanel 206 as opposed to being directed out the back.

[0055] As discussed above, minimizing power consumption by a backlightis important in order to prolong the amount of time a battery powereddevice can operate before the battery needs to be charged or replaced.

[0056] In most portable computer devices, backlight intensity iscontrolled by a user accessible control, e.g., a potentiometer. In mostknown computer devices, the brightness of the backlight is fixed at theintensity determined by the user. As ambient light conditions change,e.g., the intensity of light impinging on the front of the displayscreen decreases, it may be possible to decrease the intensity of thebacklight, and thus save power, without having a substantial negativeimpact on the readability of the displayed images. Unfortunately, mostportable computer users are unwilling to manually adjust the brightnessof the display each time ambient light conditions change resulting inthe wastage of power. Power wastage occurs from setting the brightnesscontrol higher than is required so that frequent adjustments to adisplay's brightness need not be made.

[0057] The inventors of the present application recognized that byautomating all or part of the backlight intensity adjustment process, totake into consideration changes in ambient light conditions, powersavings could be achieved. In accordance with one power saving featureof the present invention a photo-sensor is used to measure the intensityof light impinging on at least a portion of the front of a displayscreen. The result of this light measurement is then used to controlbacklight intensity. By measuring ambient light conditions and adjustingbacklight intensity, e.g., at power up and/or periodically during use,the intensity of the backlight is adjusted so that it does notsignificantly exceed a level required to display images in a mannerdeemed suitable by a user of the system. A user may indicate the desireddegree of contrast between the incident light and the light output by adisplay by manually adjusting a brightness control. By automaticallyadjusting backlight intensity as a function of ambient light conditions,power savings can be achieved. User selectable normal and power savingmodes of operation are easily supported. In the power saving mode aminimal backlight intensity is maintained as a function of detectedlight conditions. During normal mode operation a somewhat brighterscreen appearance is maintained.

[0058]FIG. 12 illustrates a portable computer 500 implemented inaccordance with one exemplary embodiment of the present invention. Theportable computer 500 comprises a base portion 506, keyboard 507 and ahinge 508. The hinge 508 attaches a display comprising a backlight 510,diffuser 509, transmissive display panel 206 and a photo-sensor 502. Thephoto-sensor 502 is mounted on the front of the display panel 206 sothat the intensity of light falling on the front of the display panel206 can be measured.

[0059] The portable computer 500, further comprises a backlightintensity control circuit 503 and a brightness control circuit 504 whichare used to control the amount of power supplied to the backlight 510and thus the intensity of light supplied to the rear of the displaypanel 206. The intensity control circuit may be implemented usingsoftware routines executed by a CPU included in the base portion 506.The brightness control circuit 504 may be implemented as a potentiometerwhich has one terminal coupled to a power supply represented by thesymbol PS and another terminal coupled to the intensity control circuit503. A user may adjust the potentiometer, e.g., by turning a knob,thereby adjusting the brightness control signal supplied to theintensity control circuit 503.

[0060] The intensity control circuit 503 determines the amount of powersupplied to the backlight 510 as a function of the output of thephoto-sensor 502 and the received brightness control signal. Theintensity of the backlight 510, as a function of the photo-sensors andbrightness control outputs, is adjusted so that the perceived brightnessof the display will remain generally constant despite changes in ambientlight conditions. Accordingly, when the output of the photo-sensor 502indicates an increase in the intensity of the ambient light striking thescreen 206, the power to the backlight 510 will be increased. As theintensity of the ambient light striking the screen 206 decreases, theintensity control circuit decreases the power supplied to the backlight510 and thus the intensity of the light output therefrom. A minimumpower level is set, e.g., pre-programmed, for the backlight 510 toinsure that the display will be readable in low light conditions.

[0061] In one embodiment, even if the output of the photo-sensor 502indicates little or no incident light, the intensity control circuit 503does not lower the power output to the backlight 510 below a preselectedthreshold to insure that in dark or dimly lit conditions, images on thedisplay panel 206 will remain visible. In such an embodiment, intensitycontrol circuit 503 maintains backlight light output between a minimumthreshold level and full intensity as a function of the output of thephoto-sensor 502 and the brightness control circuit 504.

[0062]FIG. 13 illustrates a transmissive display 501 which uses naturalor ambient light, in accordance with the present invention, tosupplement light provided, when required, by a backlight 207. Thestructure of the display 501 is similar to that of the display 302.However, to insure energy efficient control of the backlight 207, thedisplay 501 includes a front photo-sensor 502, a rear photo-sensor 512,an intensity control circuit 505 and a manual brightness control device504. In the FIG. 13 embodiment, the intensity control circuit 505receives signals indicating the amount of light shining on the rear ofthe display panel 206 from the rear photo-sensor 512 and the amount oflight shining on the front of the display panel 502. In order tomaintain the brightness at the user selected level, indicated by theoutput of the control device 504, the intensity control circuit adjuststhe amount of power supplied to the backlight 207 so that the differencebetween the signals generated by the front and rear photo-sensors 502,512 remains constant, or relatively constant, despite changes in ambientlight conditions.

[0063] While the rear photo-sensor is shown inside the display housingso that it measures the light, including the light from the backlight207, impinging on the rear of the display panel 206, it is contemplatedthat the intensity control may be performed as a function of ameasurement of light impinging on the exterior rear of the housing,e.g., on or near the diffuser 208. In one particular embodiment,backlight control is achieved using signals received from a frontphoto-sensor 502 and a rear photo-sensor 512 positioned on the exteriorof the display 501. Such an embodiment is possible since the amount oflight which will be generated by the backlight 207, given a particularpower input, can be predicted with reasonable certainty in mostmonitors.

[0064]FIG. 14 illustrates a portable computer system 503 which issimilar in construction to the previously described computer system 400.Unlike the computer system 400, the computer system 503 includes frontand rear display panel sensors 502, 512, a backlight intensity controlcircuit 505 and a manual brightness control circuit 504. The variouscomponents operate as described above to adjust backlight intensity as afunction of the measured intensity of ambient light incident on the rearof the display panel and the measured intensity of ambient light on thefront of the display panel. In the FIG. 14 embodiment, the photo-sensor512 is mounted on an exterior portion of transmissive diffuser 208 or ona portion of a display housing 504 (see FIG. 15) used to mount thepanels 206, 208. Accordingly, in such an embodiment, the photo-sensor512 detects ambient light reflected by the reflector 210 towards therear of the display panel 206.

[0065]FIG. 15 is a frontal view of the computer system 503 illustratedin FIG. 14. From this view, a display housing 504 used to mount thepanels 206, 208 and photo-sensor 502, is visible. In the FIG. 15embodiment, the display housing 504 is used to mount the frontphoto-sensor 502.

[0066] While the photo-sensors 502, 512 have been illustrated in somefigures as protruding from the surfaces on which they are mounted, it isto be understood that they may be flush mounted to facilitate foldingand storage of the display device into which they are incorporated. Inaddition, it is to be understood that the intensity control circuit 505and brightness control circuit 504 may be located internal to thehousing 406.

[0067] It should also be noted that the computer system 503 may includea central processing unit (CPU), a memory device and various softwareroutines which are stored in the memory device and executed by the CPU.The intensity control circuit 505 may be implemented using softwarewhich controls the intensity of the backlight 510 as a function of thevarious input signals which are shown as being supplied to the intensitycontrol circuit 505. In fact, the intensity control function may beincorporated into, and/or be implemented as, operating system routinesexecuted by the CPU included in the computer 500.

[0068] While numerous exemplary embodiments of the methods and apparatusof the present invention have been described above, it will be apparentto one of ordinary skill in the art, in view of the above description ofthe invention, that numerous additional embodiments are possible withoutvarying from the scope of the invention.

What is claimed is:
 1. A method of displaying an image using atransmissive display panel having a front viewing surface and a rearnon-viewing surface, comprising the steps of: directing ambient lightfrom behind a the transmissive display panel to the rear non-viewingsurface of said transmissive display panel; and controlling thetransmissive display panel to block some o f the directed ambient lightfrom passing through the transmissive display panel.
 2. The method ofclaim 1, wherein said ambient light is a natural light source locatedexternal to the transmissive display panel.
 3. The method of claim 1,further comprising the step of: using a diffuse reflector to direct theambient light.
 4. The method of claim 3, further comprising the step of:using a diffuser to diffuse the ambient light directed to the rearnon-viewing surface of said transmissive display panel.
 5. The method ofclaim 3, further comprising the step of: attaching the diffuse reflectorto the display panel using a hinge.
 6. The method of claim 1, furthercomprising the step of: using a backlight to supplement the ambientlight directed to the rear non-viewing surface of the display panel. 7.The method of claim 6, wherein the display panel includes at least oneliquid crystal cell.